PM / hibernate: Avoid overflow in hibernate_preallocate_memory()

When system has a lot of highmem (e.g. 16GiB using a 32 bits kernel),
the code to calculate how much memory we need to preallocate in
normal zone may cause overflow. As Leon has analysed:

 It looks that during computing 'alloc' variable there is overflow:
 alloc = (3943404 - 1970542) - 1978280 = -5418 (signed)
 And this function goes to err_out.

Fix this by avoiding that overflow.

References: https://bugzilla.kernel.org/show_bug.cgi?id=60817
Reported-and-tested-by: Leon Drugi <eyak@wp.pl>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index 98c3b34a4cff..10c22cae83a0 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -1402,7 +1402,11 @@ int hibernate_preallocate_memory(void)
          * highmem and non-highmem zones separately.
          */
         pages_highmem = preallocate_image_highmem(highmem / 2);
-        alloc = (count - max_size) - pages_highmem;
+        alloc = count - max_size;
+        if (alloc > pages_highmem)
+                alloc -= pages_highmem;
+        else
+                alloc = 0;
         pages = preallocate_image_memory(alloc, avail_normal);
         if (pages < alloc) {
                 /* We have exhausted non-highmem pages, try highmem. */